Tubes, valves, seals, containers, tanks, receivers, pressure vessels, pipelines, conduits, heat exchangers, and other similar components, are typically configured to retain and/or transport fluids under pressure. For purposes of this application, these different components are referred to as a pressure system and comprise one or more of the above components and their equivalents and, optionally, include other components. A non-limiting example of a pressure system includes a pipeline for transporting natural gas or other hydrocarbons. Another non-limiting example is a natural gas and/or oil well and/or wells of other types, whether being actively drilled or already producing, that typically transports fluids from the producing geological formation to a well head. Such a well includes one or more of the following components: a Christmas tree or well head; production tubing; casing; drill pipe; blowout preventers; completion equipment; coiled tubing; snubbing equipment; and other similar and typical components. Yet another non-limiting example includes hydraulic and fuel lines of various types for transporting fluids for use in mechanical devices. Yet another non-limiting example includes storage containers for retaining fluids therein. Other pressure systems fall within the scope of the disclosure.
The fluids retained or transported within pressure systems typically include one or more gases, liquids, or combinations thereof, including any solid components entrained within the fluid. As one non-limiting example, a typical fluid comprises methane or natural gas, carbon dioxide, hydrogen sulfide, natural gas liquids, water, and the like. Another non-limiting example is crude oil, which typically includes methane, propane, octane, and longer-chained hydrocarbons, including heavy oil/asphaltenes. Yet another non-limiting example is hydraulic fluid within a hydraulic line.
Pressure systems and/or the individual components that comprise the system, typically are tested to ensure that the pressure system is not leaking and/or the pressure system is capable of maintaining pressure integrity. For example, a pressure system typically is tested to provide assurance that the fluid system is capable of retaining the fluid held therein at a selected pressure (e.g., a maximum pressure rating or maximum rated pressure) without the fluid leaking or escaping from the pressure system.
It is understood that in connection with fluids and gases that exhibit a potentially significant change in pressure as a function of the fluid's temperature, it can be difficult to determine whether a change in pressure, typically, although not necessarily, a decrease in pressure, in a pressure system is merely a result of the change in temperature of the fluid, or if it is a result of a leak somewhere within the pressure system. For example, a fixed volume of a synthetic drilling fluid in a suitable container/pressure vessel used in oil and gas drilling exhibits a decreasing pressure as a function of temperature. Depending on the drilling fluid involved, the pressure can very significantly with temperature. In deepwater offshore drilling in which the drilling fluid at a temperature of between 80° F. to 120° F. at the surface, the temperature fluctuation can be quite large. For example, the fluid cools as it passes from the drilling platform, through drill pipe and/or the riser that is surrounded by the ocean, to a wellhead or blow-out preventer that can be several thousand feet below the surface of the ocean and on the sea floor where the ambient, surrounding water temperature might be as low as 34° F. Thus, there is a large and rapid transfer of heat energy from the drilling fluid, through the containing drill pipe and/or riser, to the surrounding ocean, which, in turn, causes a sometimes significant decrease in the pressure of the fluid held within the pressure system. A problem is to distinguish this drop in pressure caused by the decrease in temperature from a drop in pressure caused by a leak within the pressure system that is allowing the fluid held therein to escape.
To solve this problem of distinguishing the cause of the drop in pressure, operators of pressure systems often frequently hold a test pressure within the pressure system for a significant period of time, ranging from 10 minutes to well over an hour, until a steady-state test pressure (i.e., one in which the test pressure changes very little with time) is reached. That is, it may be only after a steady-state pressure is reached that an operator might be assured that a decrease in pressure was a result of the fluid cooling via a transfer of heat from the fluid to the sea and/or other surrounding media rather than because of a leak.
In addition, tests may be repeated several times to rule out various factors that affect the test results, such as how steadily the test fluid is added, mistakes in the test procedure, additional confirmation for assurance, and the like. The result is that significant and, often unnecessary, time is spent performing the leak/pressure tests. This is very expensive because the tests could take from 12 to 24 hours to complete when, for example, an offshore drilling vessel or rig that leases for $800,000 per day. Thus, significant savings in time and money can be made if a more efficient and accurate system and method of detecting leaks is found.
Other methods, including those that require complex calculus, differential equations that calculate an equation to fit observed data, and the like, have been proposed to reduce the time it takes to conduct a leak/pressure test. These older tests, however, typically rely on models that require accurate entry of various details of the pressure system, meticulous test protocols that must be adhered to strictly; and highly trained personal. In turn such systems can be impractical in many applications.
Thus, there exists a need for a system that can accurately perform a leak/pressure test, particularly for fluids including gases that demonstrate a change in pressure with a change in temperature, that is simple, and does not require complex models or sufficient data to solve differential equations.